Stents and catheters having improved stent deployment

ABSTRACT

An implant delivery system and method comprises an implant, for example, a stent, and a delivery catheter. The stent has a scaffold with a coating or a shell that retains the scaffold in a collapsed configuration. The coating or shell is made of a material that dissolves or biodegrades upon exposure to a dissolution or biodegradation media. The stent is used with an implant delivery system which has a catheter with a catheter, wherein the stent is mounted on the catheter shaft. The catheter shaft is configured to be withdrawn through the patient&#39;s vessel when the scaffold is in its expanded configuration. Advantageously, the implant is thereby prevented from changing length during implant delivery and implant deployment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser.No. 61/095,766, filed Sep. 10, 2008, the entire content of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to systems for delivering an implant to asite in a body lumen. More particularly, this invention pertains todelivery systems for a vascular implant such as a self-expanding stent.

BACKGROUND OF THE INVENTION

Stents are widely used for supporting a lumen structure in a patient'sbody. For example, stents may be used to maintain patency of a coronaryartery, carotid artery, cerebral artery, femoral artery, other bloodvessels including veins, or other body lumens such as the ureter,urethra, bronchus, esophagus, or other passage.

Stents are commonly metallic tubular structures made from stainlesssteel, Nitinol, Elgiloy, cobalt chrome alloys, tantalum, and othermetals, although polymer stents are known. Stents can be permanentenduring implants, or can be bioabsorbable at least in part.Bioabsorbable stents can be polymeric, bio-polymeric, ceramic,bio-ceramic, or metallic, and may elute over time substances such asdrugs. Non-bioabsorbable stents may also release drugs over time. Stentsare passed through a body lumen in a collapsed state. At the point of anobstruction or other deployment site in the body lumen, the stent isexpanded to an expanded diameter to support the lumen at the deploymentsite.

In certain designs, stents are comprised of tubes having multiplethrough holes or cells that are expanded by inflatable balloons at thedeployment site. This type of stent is often referred to as a “balloonexpandable” stent. Stent delivery systems for balloon expandable stentsare typically comprised of an inflatable balloon mounted on a two lumentube. The stent delivery system with stent compressed thereon can beadvanced to a treatment site over a guidewire, and the balloon inflatedto expand and deploy the stent.

Other stents are so-called “self expanding” stents and do not useballoons to cause the expansion of the stent. An example of aself-expanding stent is a tube (e.g., a coil of wire or a tube comprisedof cells) made of an elastically deformable material (e.g., asuperelastic material such a nitinol). Some self expanding stents arealso comprised of tubes having multiple through holes or cells. Thistype of stent is secured in compression in a collapsed state to a stentdelivery device. At the deployment site, stent compression is releasedand restoring forces within the stent cause the stent to self-expand toits enlarged diameter.

Other self-expanding stents are made of so-called shape-memory metals.Such shape-memory stents experience a phase change at the elevatedtemperature of the human body. The phase change results in expansionfrom a collapsed state to an enlarged state.

A very popular type of self expanding stent is a cellular tube made fromself-expanding nitinol, for example, the EverFlex stent from ev3, Inc.of Plymouth, Minn. Cellular stents are commonly made by laser cutting oftubes, or cutting patterns into sheets followed by or preceded bywelding the sheet into a tube shape, and other methods. Another deliverytechnique for a self expanding stent is to mount the collapsed stent ona distal end of a stent delivery system. Such a system can be comprisedof an outer tubular member and an inner tubular member. The inner andouter tubular members are axially slideable relative to one another. Thestent (in the collapsed state) is mounted surrounding the inner tubularmember at its distal end. The outer tubular member (also called theouter sheath) surrounds the stent at the distal end.

Prior to advancing the stent delivery system through the body lumen, aguide wire is first passed through the body lumen to the deploymentsite. The inner tube of the delivery system is hollow throughout atleast a portion of its length such that it can be advanced over theguide wire to the deployment site. The combined structure (i.e., stentmounted on stent delivery system) is passed through the patient's lumenuntil the distal end of the delivery system arrives at the deploymentsite within the body lumen. The deployment system and/or the stent mayinclude radiopaque markers to permit a physician to visualizepositioning of the stent under fluoroscopy prior to deployment. At thedeployment site, the outer sheath is retracted to expose the stent. Theexposed stent is free to self-expand within the body lumen. Followingexpansion of the stent, the inner tube is free to pass through the stentsuch that the delivery system can be removed through the body lumenleaving the stent in place at the deployment site.

In prior art devices, high forces may be required to retract the outersheath so as to permit the stent to self expand. Delivery systemsdesigned to withstand high retraction forces can be bulky, can havereduced flexibility and can have unacceptable failure rates. Inaddition, due to frictional forces between the stent and the outersheath in prior art devices the stent may change in length duringdeployment, either in overall length or locally over regions of thestent. For example, long stents, thin stents, stents with high axialflexibility parallel to the central axis of the stent, or stents with alarge amount of expansile force, when compressed in a sheath, tend tochange in length as the outer sheath is withdrawn from the inner tubularmember. Also, prior art delivery systems can be moved when the implantis partially deployed, resulting in undesirable regional length changesin the implanted device. Changes in stent length during stent deploymentcan prevent a stent from being properly deployed over the intendedtreatment area, can compromise stent fracture resistance and cancompromise stent fatigue life.

What is needed is a stent delivery system that permits low force andprecise delivery of stents without altering the intended length of thestent.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a stent includes ascaffold and a coating that restrains diametrical expansion of thescaffold. Dissolution or biodegradation of the coating allows the stentto expand or be expanded.

According to another aspect of the present invention, a stent includes ascaffold and a shell that restrains diametrical expansion of thescaffold. Dissolution or biodegradation of the shell allows the stent toexpand or be expanded.

According to other aspects of the present invention, an implant deliverysystem includes a stent with a scaffold and a coating or shell thatrestrains diametrical expansion of the scaffold and a catheter on whichthe stent is mounted in a collapsed, restrained state. Upon exposure todissolution fluid or biodegradation media, dissolution or biodegradationof the coating or shell allows the stent to expand or be expanded.

According to other aspects of the present invention, an implant deliverysystem includes a stent with a scaffold and a coating that restrainsdiametrical expansion of the scaffold and an inflatable balloon mountedon the catheter beneath the stent. Upon inflating the balloon thecoating or shell is compromised or fractured and the stent self-expandsor is further expanded by further inflation of the balloon. Exposure todissolution fluid or biodegradation media causes fragments of thecoating or shell to dissolve or biodegrade.

According to other aspects of the present invention, an implant deliverysystem includes a stent with a scaffold and a coating that restrainsdiametrical expansion of the scaffold and a slidable tubular sheathsurrounding the catheter and restrained stent. Upon proximal withdrawalof the sheath the coating or shell is exposed to dissolution fluid orbiodegradation media and dissolution or biodegradation of the coating orshell allows the stent to expand or be expanded. Exposure to dissolutionfluid or biodegradation media causes fragments of the coating or shellto dissolve or biodegrade.

According to yet other aspects of the present invention, an implantdelivery system includes a stent with a scaffold and a coating thatrestrains diametrical expansion of the scaffold, and a slidable tubularsheath surrounding the catheter, an inflatable balloon and a restrainedstent. The stent is deployed by proximal withdrawal of the sheathfollowed by inflation of the balloon to compromise or fracture thecoating or shell. The stent then self-expands or is further expanded byfurther inflation of the balloon. Exposure to dissolution fluid orbiodegradation media causes fragments of the coating or shell todissolve or biodegrade.

In yet another aspect of the present invention, an implant deliverysystem having a stent with a scaffold and a coating that restrainsdiametrical expansion of the scaffold is delivered to a treatment site,a slidable tubular sheath surrounding the catheter, an inflatableballoon and a restrained stent, is delivered to a treatment site. At thetreatment site, the balloon is inflated until the sliding friction ofthe stent against the balloon is greater than the sliding friction ofthe stent against the outer sheath. The outer sheath is then retractedto expose the stent which self expands upon exposure. The stent may befurther expanded by further inflation of the balloon.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which:

FIG. 1A illustrates a schematic side view of an implant delivery systemhaving features in accordance with the principles of the presentdisclosure;

FIGS. 1B, 1C and 2 illustrate schematic cross sectional views of stentand stent implant system embodiments having features in accordance withthe principles of the present disclosure;

FIGS. 3A to 3C, 4, and 5A to 5D illustrate schematic cross sectionalviews of implant delivery systems having features in accordance with theprinciples of the present disclosure;

FIGS. 6A, 6B, 6C, 7, 8A, 8B, 8C and 8D illustrate schematic side viewsof implant delivery systems having features in accordance with theprinciples of the present disclosure.

DETAILED DESCRIPTION

Embodiments that are examples of how inventive aspects in accordancewith the principles of the present invention will now be described inmore detail with reference to the drawings. It is to be understood thatboth the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the broad inventive aspects disclosed herein. It will also beappreciated that the inventive concepts disclosed herein are not limitedto the particular stent configurations disclosed herein, but are insteadapplicable to any number of different stent configurations.

FIGS. 1A and 1B illustrate implant delivery system 1 comprised of stent10, catheter shaft 5 with hub 3 and guidewire lumen 6 extending throughcatheter shaft and hub. Catheter shaft 5 is relatively flexible, may becomprised of a polymeric material such as nylon or PEBAX, and may rangein length from 60 cm to 300 cm. Catheter outside diameter may range fromabout 2 Fr to about 10 Fr. Guidewire lumen 6 diameter may be largeenough to allow passage of guidewires ranging in diameter from 0.009″ to0.038″. Hub 3 is sealingly attached to catheter shaft 5, is adapted toreversibly connect to other medical devices (for example by means of aluer fitting) and may be comprised of polycarbonate. Stent 10 iscomprised of scaffold 12 and coating 14. In various embodiments scaffoldmay be self expanding, balloon expandable, tubular, comprised of cells,comprised of coils, comprised of metals, polymer, ceramics, or othermaterials, or may have other characteristics. In one embodiment scaffold12 includes Nitinol tubing having cellular openings and having suitableheat treatment to cause scaffold 12 to self-expand at human bodytemperatures. Scaffold 12 configurations suitable for the inventioninclude but are not limited to tapered, flared, braided, bifurcated,fracturable, mesh covered, scaffolds comprised of radiopaque markers,and other scaffolds as are known in the art. Long scaffolds areespecially suited to the invention. Implant delivery systems 1 forscaffolds having lengths of from 20-400 mm are contemplated. In oneembodiment, implant delivery system 1 can deliver and deploy a 30 mmscaffold. In other embodiments, implant delivery system 1 can deliverand deploy a 40 mm, 60 mm, 80 mm, 100 mm, 120 mm, 150 mm, 180 mm, 200mm, 250 mm, 300 mm or 350 mm scaffold. As shown in FIGS. 1B and 1C,coating 14 may optionally be applied to catheter shaft 5 outer diameteralong some or all of the scaffold length and may be applied to at leastone of outer surface, inner surface, or through thickness of scaffold12. In some embodiments coating 14 covers the exposed edges of stent 10so as to form a smooth exterior coated stent surface. Coating 14, whenapplied and hardened, maintains stent 10 at an unexpanded diameter and afixed length prior to stent deployment. Coating 14 may cause stent toadhere directly to inner member. Coating 14 may be comprised ofbiodegradable materials, or may be comprised of materials that dissolvein the body or in the bloodstream. In some embodiments coating 14includes sugar, carbowax, polyethylene oxide, poly vinyl alcohol orother materials. Coating 14 may be applied by spray, dip, or otherprocesses to unexpanded stent and allowed to harden, may be applied toexpanded stent and allowed to harden after stent is compressed, may beapplied to and hardened on expanded stent so as to maintain scaffold inan unexpanded diameter after subsequent stent compression, or may beapplied and hardened by other methods.

In some embodiments coating 14 can dissolve or biodegrade over time soas to release the scaffold. In some embodiments coating 14 can dissolveor biodegrade when in contact with blood to allow expansion of scaffold12. Upon contact with dissolution or biodegradation causing media,scaffold release times of 0.5 to 300 seconds are contemplated. In oneembodiment, scaffold release time is approximately 1 second. In otherembodiments, scaffold release time is approximately 2, 5, 10, 20, 30,45, 60, 90, 120, 150, 180 or 240 seconds. In some embodiments a changein scaffold 12 length of less than 10% upon expansion from a contractedto an expanded configuration is contemplated. In other embodiments,scaffold 12 length change upon expansion from a contracted to anexpanded configuration is less than 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or1%.

Coating 14 may be comprised of bioactive materials such asantirestenotic agents, anti-inflammatory agents, antithrombotic agents,antiatheromatic (antiatheroma) agents, antioxidative agents, or otheragents. Bioactive coating materials may be released from the coatinginto surrounding tissue or blood and may have a diagnostic ortherapeutic action on tissue or blood.

An exemplary method of using a stent 10 with implant delivery system 1is now described. A guidewire is advance into a patient's femoral arteryusing known techniques, through a patient's vessel and past a treatmentsite. Stent 10 is loaded onto implant delivery system 1 and introducedover the guidewire into the patient's vessel. Stent 10 is restrainedfrom expanding by coating 14. The stent and implant delivery systemcombination is advanced over the guidewire and through the patientsvessel until stent 10 is located at a treatment site, for example withina stenosis in a femoral artery. Stent 10 is deployed by allowing coating14 to dissolve or to biodegrade thereby allowing scaffold 12 toself-expand. Catheter shaft 5 is then withdrawn through the patient'svessel and out of the patient's body. Any of coating that is pinnedbetween scaffold and the vessel, attached to scaffold, or whichembolizes from the treatment site dissolves or biodegrades over time.Scaffold 10 does not change length upon deployment because the scaffoldis immobilized on catheter shaft 5 by coating 14 during delivery to thetreatment site and because there is no sheath to draw past the stentduring deployment.

FIG. 2 illustrates implant delivery system 1 comprised of stent 20,catheter shaft 5 with hub (not shown) and guidewire lumen 6 extendingthrough catheter shaft and hub. Stent 20 includes scaffold 12 and shell24. Shell 24 surrounds scaffold 12 and may form a smooth exteriorsurface over stent 20. Shell 24 maintains stent 20 at an unexpandeddiameter prior to stent deployment and may be comprised of biodegradablematerials, or may be comprised of materials that dissolve in the body orin the bloodstream. In some embodiments shell 24 includes sugar,carbowax, polyethylene oxide, poly vinyl alcohol, poly lactic acid(PLA), poly glycolic acid (PGA), poly lactic glycolic acid (PLGA), poly(c-caprolactone) copolymers, polydioxanone, poly(propylene fumarate)poly(trimethylene carbonate) copolymers, polyhydroxy alkanoates,polyphosphazenes, polyanhydrides, poly(ortho esters), poly(amino acids),or “pseudo”-poly(amino acids).

The resorption or dissolution time of shell 24 can be varied by varyingthe ratio of constituent materials or by other means. The shell materialmay be axially or biaxially oriented or may have other structure. Shell24 may be comprised of tubing into which scaffold 12 is inserted, or offilm which is wrapped around compressed scaffold, or other structures,and may be applied by other application methods. Shell may be slit,perforated, have a high ability to stretch, may soften abruptly orsubstantially when heated to near body temperature, or have othercharacteristics to aid with shell fracture during scaffold expansion.

In some embodiments shell 24 can dissolve or biodegrade over time so asto release scaffold. In some embodiments shell 24 can dissolve orbiodegrade when in contact with blood to allow expansion of scaffold 12.Upon contact with dissolution or biodegradation causing media, scaffoldrelease times of 0.5 to 300 seconds are contemplated. In one embodiment,the scaffold release time is approximately 1 second. In otherembodiments, the scaffold release time is approximately 2, 5, 10, 20,30, 45, 60, 90, 120, 150, 180 or 240 seconds. In some embodiments achange in scaffold 12 length of less than 10% upon expansion from acontracted to an expanded configuration is contemplated. In otherembodiments, scaffold 12 length change upon expansion from a contractedto an expanded configuration is less than 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%or 1%.

Shell 24 may be comprised of bioactive materials such as antirestenoticagents, anti-inflammatory agents, antithrombotic agents, antiatheromatic(antiatheroma) agents, antioxidative agents, or other agents. Bioactivecoating materials may be released from the coating into surroundingtissue or blood and may have a diagnostic or therapeutic action ontissue or blood.

An exemplary method of using a stent 20 with implant delivery system 1is now described. A guidewire is advance into a patient's femoral arteryusing known techniques, through a patient's vessel and past a treatmentsite. Stent 20 is loaded onto implant delivery system 1 and introducedover the guidewire into the patient's vessel. Stent 20 is restrainedfrom expanding by shell 24. The stent and implant delivery systemcombination is advanced over the guidewire and through the patientsvessel until stent 20 is located at a treatment site, for example withina stenosis in a carotid artery. Stent 20 is deployed by allowing shell24 to dissolve or to biodegrade thereby allowing scaffold toself-expand. Shell may fracture upon expansion of scaffold, and suchfracture may be assisted by preplaced slits, slots, local thinning ofwall thickness of shell, or other means. Catheter shaft 5 is thenwithdrawn through the patient's vessel and out of the patient's body.Any of shell 24 that is pinned between scaffold and the vessel, attachedto scaffold, or which embolizes from the treatment site dissolves orbiodegrades over time. Scaffold 12 does not change length on deploymentbecause the scaffold is immobilized on catheter shaft 5 during deliveryto the treatment site and because there is no sheath to draw past thestent during deployment

FIGS. 3A to 3C illustrate an example of a Rapid Exchange (RX) deliverysystem 30 comprised of stent 32, catheter shaft 35 having ballooninflation lumen (not shown), guidewire lumen 36, guidewire lumen exitskive 39 and inflation hub 33, and balloon 31. Catheter shaft 35 isrelatively flexible, may be comprised of a polymeric material such asnylon or PEBAX, and may range in length from 60 cm to 300 cm. Cathetershaft 35 outside diameter may range from about 2 Fr to about 10 Fr.Guidewire lumen 36 diameter may be large enough to allow passage ofguidewires ranging in diameter from 0.009″ to 0.038″. Hub 33 issealingly attached to catheter shaft 35, is adapted to reversiblyconnect to other medical devices (for example by means of a luerfitting) and may be comprised of polycarbonate. Balloon 31 is sealinglyattached at both proximal and distal ends to catheter shaft 35 and maybe comprised of biaxially oriented nylon, polyester, Pebax, polyolefin,or other materials. Stent 32 may be comprised of stents 10, 20 or otherstents, is shown in an unexpanded configuration in FIGS. 3A and 3B andin an expanded configuration in FIG. 3C. Stent 32 is deployed byconnecting an inflation device (not shown) to hub 33 and pressurizingballoon inflation lumen with fluid or gas so as to expand balloon 31thereby expanding stent 32. In some embodiments stent 32 is fullyexpanded into contact with vessel wall by expansion of balloon 31.

When balloon 31 is expanded beneath stent 10, the restraining force ofcoating 14 is overcome by balloon pressure and the coating fractures,allowing stent 10 to expand. When balloon 31 is expanded beneath stent20, the restraining force of shell 24 is overcome by balloon pressureand the shell fractures, allowing stent 20 to expand.

An exemplary method of using stent 32 with delivery system 30 is nowdescribed. A guidewire is advanced into a patient's femoral artery usingknown techniques, through a patient's vessel and past a treatment site.A stent 32 (for example stent 10, 20) is loaded onto implant deliverysystem 30 and introduced over the guidewire into the patient's vessel.The stent and implant delivery system combination is advanced over theguidewire and through the patient's vessel until the stent is located ata treatment site, for example within a stenosis in a carotid artery.Stent 10, 20 is deployed by inflating balloon 31 thereby causing coating14 or shell 24 to fracture and stent to expand. Catheter 35 is thenwithdrawn through the patient's vessel and out of the patient's body.Any of coating or shell that is pinned under scaffold, or whichembolizes, dissolves/degrades over time. Stent 10, 20 does not changelength on deployment because the stent is immobilized on catheter shaft35 during delivery to the treatment site and because there is no sheathto draw past the stent during deployment.

FIG. 4 illustrates an example of an Over The Wire (OTW) delivery system40 comprised of stent 42, catheter shaft 45 having balloon inflationlumen (not shown), guidewire lumen (not shown) and manifold 47, andballoon 41. Manifold 47 includes guidewire lumen exit port 49 andinflation hub 43. Catheter shaft 45, guidewire lumen, balloon 41, andinflation hub 43 have substantially the same construction, dimensions,and function as catheter shaft 35, guidewire lumen 36, balloon 31, andinflation hub 33 described above in conjunction with FIGS. 3A to 3C.Manifold 47 is sealingly attached to catheter shaft 45 and may becomprised of polycarbonate. Guidewire lumen exit port 49 and inflationhub 43 are adapted to reversibly connect to other medical devices (forexample by means of a luer fitting). (for example stent 10, 20), Stent42 may be comprised of stents 10, 20 or other stents and is shown in anexpanded configuration in

FIG. 4. Stent 42 is deployed by connecting inflation device (not shown)to hub 43 and pressurizing balloon inflation lumen with fluid or gas soas to expand balloon 41 thereby expanding stent 42. In some embodimentsstent 42 is fully expanded into contact with vessel wall by expansion ofballoon 41.

The methods of using and the benefits of using Over The Wire (OTW)delivery system 40 are substantially the same as those described abovefor Rapid Exchange (RX) delivery system 30.

FIGS. 5A, 5B, 5C and 5D illustrate further embodiments of implantdelivery systems having features in accordance with the principles ofthe present disclosure. FIG. 5A illustrates implant delivery system 50comprised of implant delivery system 30, 40 with modifications to thedistal balloon containing portion of implant delivery system 30, 40.Proximal region of system 50 includes catheter shaft 35, 45 havingballoon inflation lumen 51 a and guidewire lumen 55 a, inflation hub 33,43 (not shown) and either guidewire lumen exit skive 39 (not shown) incatheter shaft 35 or manifold 47 (not shown) attached to catheter shaft45 as described above for systems 30, 40. Distal region of system 50includes catheter shaft 35, 45, balloon 51, stent 52, band 56 a andadhesive 54. Balloon 51 is sealingly attached to catheter shaft 35, 45at proximal and distal bonds 51 p, 51 d and may be comprised ofcompliant, semi compliant, non-compliant, or low pressure balloonmaterials and may be comprised of biaxially oriented nylon, polyester,Pebax, polyolefin, or other materials. In some embodiments balloon 51includes highly elastic materials such as polyurethane elastomers.

Stent 52 may be comprised of stent 10, stent 20, or any stent to whichadhesive 54 can bond. For example, stent 54 configurations suitable forthe invention include but are not limited to cellular stents,fracturable stents, coil stents, covered stents, stent grafts, meshcovered stents, tapered stents, flared stents, braided stents,bifurcation stents, and other stents as are known in the art. Longstents are especially suited to the invention. Implant delivery systems50 for stents having lengths of from 20 to 400 mm are contemplated. Inone embodiment, a stent delivery system 50 can deliver and deploy a 30mm stent. In other embodiments, a stent delivery system 50 can deliverand deploy a 40 mm, 60 mm, 80 mm, 100 mm, 120 mm, 150 mm, 180 mm, 200mm, 250 mm, 300 mm or 350 mm stent.

Band 56 a is attached to catheter shaft 35, 45 by friction fit and maybe comprised of materials such as metal, Elgiloy, platinum, platinumalloy, nickel-titanium alloy, engineering polymer, liquid crystalpolymer, polyester, nylon, or other materials. Edges of band are roundedso as to not promote balloon burst upon balloon inflation. Band 56 asandwiches balloon 51 between band and catheter shaft. Band isconfigured to allow inflation of the portion of balloon 51 that does notunderlie band 56 a. In one embodiment band 56 a takes the form of acoiled ribbon. In another embodiment, outer surface of catheter 35, 45has a groove therealong to receive band 56 a. Adhesive 54 attaches stent52 to band 56 a and may be comprised of biodegradable or dissolvablematerials such as poly lactic acid (PLA), poly glycolic acid (PGA), orpoly lactic glycolic acid (PLGA), or may be comprised of EVA,polyurethane, nylon, or other materials. In some embodiments adhesiveextends into openings through wall thickness of stent 52.

In an alternate embodiment (FIGS. 5B and 5C), band 56 b includes one ormore patches or islands of material having circular, oval, irregular, orother shape and is further comprised of one or more of the materialsused to construct band 56 a. Band 56 b is bonded to balloon 51, andballoon 51 is locally bonded to catheter shaft 35, 45 in the regionunderlying band 56 b by means of heat, adhesive, or other means. Localbonds of balloon 51 to catheter shaft 35, 45 are arranged in a patternthat allows flow to inflate unbonded portion of balloon. In yet anotherembodiment (FIG. 5D), balloon is locally bonded to catheter shaft 35, 45by means of heat, adhesive, or other means over a patch or island havingcircular, oval, irregular, or other shape and band 56 c includes thebonded region or patch or island. Local bonds of balloon 51 to cathetershaft 35, 45 are arranged in a pattern that allows flow to inflateunbonded portion of balloon. Adhesive 54 attaches stent 52 to band 56 b,56 c and may be comprised of biodegradable or dissolvable materials suchas poly lactic acid (PLA), poly glycolic acid (PGA), or poly lacticglycolic acid (PLGA), or may be comprised of EVA, polyurethane, nylon,or other materials. In some embodiments adhesive extends into openingsthrough wall thickness of stent 52.

An exemplary method of using a stent 52 with implant delivery system 50is now described. A guidewire is advanced into a patient's femoralartery using known techniques, through a patient's vessel and past atreatment site. Stent 52 (for example stent 10, 20, or other stent) isloaded onto stent delivery system 50 and introduced over the guidewireinto the patient's vessel. The stent and stent delivery systemcombination is advanced over the guidewire and through the patientsvessel until the stent is located at a treatment site, for examplewithin a stenosis in a popliteal artery. Stent 52 is deployed byinflating balloon 51 thereby fracturing adhesive 54 attachments betweenband(s) 56 a, 56 b, 56 c and stent 52, causing or allowing stent toexpand. Catheter shaft 35, 45 is then withdrawn through the patient'svessel and out of the patient's body. In the case of biodegradable ordissolvable adhesive 54, any of adhesive that is pinned under stent 52,or which embolizes, dissolves or degrades over time. Stent 52 does notchange length on deployment because the stent is immobilized on cathetershaft 35 during delivery to the treatment site and because there is nosheath to draw past the stent during deployment.

FIGS. 6A, 6B, 8A, 8B, 8C and 8D illustrate RX delivery system 60comprised of implant delivery catheter 66 having distal region 80 andstent 82. Implant delivery catheter 66 includes catheter shaft 65,guidewire lumen 65 a, proximal guidewire exit skive 69, proximal handle68, sheath 84 and distal manifold 67. Proximal handle 68 is sealinglyattached to catheter shaft 65 and may be comprised of polycarbonate.Catheter shaft 65 is relatively flexible, may be comprised of apolymeric material such as nylon or PEBAX, and may range in length from60 cm to 300 cm. Catheter outside diameter may range from about 2 Fr toabout 10 Fr. Guidewire lumen 65 a diameter may be large enough to allowpassage of guidewires ranging in diameter from 0.009″ to 0.038″. Distalmanifold 67 is sealingly attached to sheath 84 and may be comprised ofpolycarbonate. Sheath 84 may be comprised of braid-reinforced polyester,non-reinforced polymers such as nylon or polyester, or other materials,and adapted to resist kinking and to transmit axial forces along itslength. Sheath 84 may be constructed so as to have varying degrees offlexibility along its length. In one embodiment (FIG. 6C) sheath 84includes seal 84 a, weep holes 84 b, or both. Seal prevents liquids andbody fluids from contacting stent 82 when sheath is fully advanced tocover stent 82, and may be constructed of elastomeric materials such aslow durometer PEBAX, polyurethane, or other materials. Weep holes 84 ballow annular space between sheath 84 and catheter shaft 65 to be purgedof air. Stent 82 may be comprised of stent 10, 20, or other stents. Insome embodiments, coating 14 or shell 24 is substantially shielded fromdissolution or biodegradation causing media due to barrier properties ofsheath in combination with sheath seal.

Optionally, implant delivery catheter 66 is further comprised of balloon81 (FIG. 8D), balloon inflation lumen within catheter 65 (not shown),and balloon inflation hub 63. Hub 63 is sealingly attached to proximalhandle 88, is adapted to reversibly connect to other medical devices(for example by means of a luer fitting) and may be comprised ofpolycarbonate. Balloon 81 is sealingly attached at both proximal anddistal ends to catheter shaft 65 and may be comprised of biaxiallyoriented nylon, polyester, Pebax, polyolefin, or other materials. In oneembodiment, balloon 81 is constructed such that the coefficient offriction of the balloon in contact with stent 82 is greater than thecoefficient of friction of sheath 84 in contact with stent 82.

FIGS. 7, 8A, 8B, 8C and 8D illustrate OTW delivery system 70 comprisedof implant delivery catheter 76 having distal region 80 and stent 82.Implant delivery catheter 76 includes catheter shaft 75, guidewire lumen(not shown), proximal guidewire exit port 79, proximal handle 78, sheath84 and distal manifold 77 a. Sheath 84 may optionally be comprised ofseal 84 a, weep holes 84 b, or both and distal manifold 77 a includesinfusion tube with stopcock 77 b. Catheter shaft 75, guidewire lumen,proximal handle 78 and distal manifold have substantially the sameconstruction, dimensions, and function as catheter shaft 65, guidewirelumen 65 a, proximal handle 68 and distal manifold 67 described above inconjunction with FIGS. 6A to 6D. Stent 82 may be comprised of stent 10,20, or other stents. In some embodiments, coating 14 or shell 24 issubstantially shielded from dissolution or biodegradation causing mediadue to barrier properties of sheath in combination with sheath seal.

Optionally, implant delivery catheter 76 is further comprised of balloon81 (FIG. 8D), balloon inflation lumen within catheter 75 (not shown),and balloon inflation hub 73. Hub 73 is sealingly attached to proximalguidewire exit port 79, is adapted to reversibly connect to othermedical devices (for example by means of a luer fitting) and may becomprised of polycarbonate. Balloon 81 is sealingly attached at bothproximal and distal ends to catheter shaft 75 and may be comprised ofbiaxially oriented nylon, polyester, Pebax, polyolefin, or othermaterials.

An exemplary method of using implant delivery system 60, 70 with stent82 is now described with the assistance of FIGS. 8A to 8C. A guidewireis advanced into a patient's femoral artery using known techniques,through a patient's vessel and past a treatment site. Stent 82 (forexample stent 10, 20) is loaded onto stent delivery system 60, 70 (FIG.8A) and introduced over the guidewire into the patient's vessel. Thestent and stent delivery system combination is advanced over theguidewire and through the patients vessel until the stent is located ata treatment site, for example within a stenosis in an iliac artery.Stent 82 is deployed by sliding proximal handle 68, 78 and distalmanifold 67, 77 a closer together, thereby causing sheath 84 to withdrawproximally and uncover stent 82 (FIG. 8B). Withdrawal of sheath fromstent 10, 20 allows blood and/or media to contact coating or shellthereby releasing stent restraint after dissolution or biodegradation ofcoating or shell, allowing stent to self-expand (FIG. 8C). Catheter 66,76 is then withdrawn through the patient's vessel and out of thepatient's body. Because the coating or shell restrains the stent fromexpanding or changing length sheath withdrawal force is reduced and thestent does not change length on deployment.

In some methods, sheath 84 is partially withdrawn from stent 82 so as toallow uncovered portion of stent to expand into contact with the vesselwall, thereby providing frictional localization of the expanded portionof the stent against the vessel wall.

In some embodiments, before dissolution or biodegradation of coating orshell an operator can advance the sheath distally so as to recapture thestent. This is possible because the coating or shell provides a smoothcovering over the structural portion of the stent such that the distalend of the sheath will not become mechanically entangled with thestructural portion. Recapture of a stent is desirable when the operatorwishes to change the eventual deployed position of the stent or forother reasons. In other embodiments, sheath seal 84 a prevents bloodand/or media to contact stent 82 during stent delivery in the patient,thereby preventing expansion of stent 82 secondary to prematuredissolution or biodegradation of coating 14 or shell 24. In still otherembodiments, prior to introduction into a patient delivery system 60, 70is flushed with fluid to purge air by connecting a syringe filled withflushing solution (e.g. saline) to distal manifold 67, 77 a and forcingflushing solution through sheath 84 and out weep holes 84 b, therebypreventing flushing fluid from contacting stent 82 and potentiallycausing premature dissolution or biodegradation of coating 14 or shell24.

In methods of using embodiments of implant delivery system 60, 70 whereballoon 81 is incorporated into the system, balloon 81 is inflated afterwithdrawal of sheath 84 (FIG. 8D) by connecting inflation device (notshown) to hub 63, 73 and pressurizing balloon inflation lumen with fluidor gas thereby causing stent 82 to expand after fracture or compromiseof coating or shell. In some embodiments stent 82 is fully expanded intocontact with vessel wall by expansion of balloon. Because the coating orshell restrains the stent from expanding or changing length and becausethe stent is expanded by balloon, sheath withdrawal force is reduced andthe stent does not change length on deployment.

An alternate exemplary method of using embodiments of implant deliverysystem 60, 70 where balloon 81 is incorporated into the system withstent 82 is now described with the assistance of FIGS. 8A to 8D. Aguidewire is advanced into a patient's femoral artery using knowntechniques, through a patient's vessel and past a treatment site. Stent82 (for example any stent that self expands when not restrained byanother device or component) is loaded onto stent delivery system 60, 70(FIG. 8A) and introduced over the guidewire into the patient's vessel.The stent and stent delivery system combination is advanced over theguidewire and through the patients vessel until the stent is located ata treatment site, for example within a stenosis in a carotid artery.Balloon 81 is inflated prior to withdrawal of sheath 84 (FIG. 8A,balloon not shown) by connecting inflation device (not shown) to hub 63,73 and pressurizing balloon inflation lumen with fluid or gas untilsliding friction of stent 82 against balloon 81 exceeds sliding frictionof stent 82 against sheath 84. Stent 82 is deployed by sliding proximalhandle 68, 78 and distal manifold 67, 77 a closer together, therebycausing sheath 84 to withdraw proximally and uncover stent 82 (FIG. 8D).Catheter 66, 76 is then withdrawn through the patient's vessel and outof the patient's body. Because the inflated balloon restrains the stentfrom changing length (for example buckling, stretching, kinking, or“bunching up”) in the sheath, sheath withdrawal force is reduced and thestent does not change length on deployment.

While the various examples of the present invention have related tostents and stent delivery systems, the scope of the present invention isnot so limited. For example, while particularly suited for stentdelivery systems, it will be appreciated that the various aspects of thepresent invention are also applicable to systems for delivering othertypes of expandable implants. By way of non-limiting example, othertypes of expanding implants include anastomosis devices, blood filters,grafts, vena cava filters, percutaneous valves, aneurism treatmentdevices, or other devices.

It has been shown how certain objects of the invention have beenattained in a preferred manner. Modifications and equivalents of thedisclosed concepts are intended to be included within the scope of theclaims. Alternate materials for many of the delivery system componentsare generally well known in the art can be substituted for any of thenon-limiting examples listed above provided the functional requirementsof the component are met. Further, while choices for materials andconfigurations may have been described above with respect to certainembodiments, one of ordinary skill in the art will understand that thematerials and configurations described are applicable across theembodiments.

1. A stent for insertion into a body lumen, comprising: a scaffoldhaving a collapsed and a diametrically expanded configuration; and acoating or a shell surrounding the scaffold that retains the scaffold inits collapsed configuration, said coating or shell made of a materialthat dissolves or biodegrades upon exposure to a dissolution orbiodegradation media; wherein the scaffold is expanded from itscollapsed to its expanded configuration through exposure of the coatingor shell to the dissolution or biodegradation media.
 2. The stent ofclaim 1, wherein the coating comprises a material selected from thegroup consisting of sugar, carbowax, polyethylene oxide, and poly vinylalcohol.
 3. The stent of claim 1, wherein the coating or shell comprisesa bioactive material selected from the group consisting ofantirestenotic agents, anti-inflammatory agents, antithrombotic agents,antiatheromatic (antiatheroma) agents, and antioxidative agents.
 4. Thestent of claim 1, wherein the shell comprises a material selected fromthe group consisting of sugar, carbowax, polyethylene oxide, poly vinylalcohol, poly lactic acid (PLA), poly glycolic acid (PGA), poly lacticglycolic acid (PLGA), poly (ε-caprolactone) copolymers, polydioxanone,poly(propylene fumarate) poly(trimethylene carbonate) copolymers,polyhydroxy alkanoates, polyphosphazenes, polyanhydrides, poly(orthoesters), poly(amino acids), or “pseudo”-poly(amino acids).
 5. The stentof claim 1, wherein the shell comprises tubing into which the scaffoldis inserted, or a film which is wrapped around the compressed scaffold.6. The stent of claim 5, wherein the shell comprises a longitudinal slitor is perforated.
 7. The stent of claim 1, wherein the scaffold isself-expanding.
 8. The stent of claim 1, wherein the scaffold isballoon-expandable.
 9. An implant delivery system for deploying a stentin a patient's vessel, the system comprising: a catheter having acatheter shaft; a stent mounted on the catheter shaft, said stentcomprising a scaffold having a collapsed configuration and adiametrically expanded configuration; and a coating or a shellsurrounding the scaffold and retaining the scaffold in its collapsedconfiguration, said coating or shell made of a material that dissolvesor biodegrades upon exposure to a dissolution or biodegradation media;wherein the scaffold is expanded from its collapsed to its expandedconfiguration through exposure of the coating or shell to thedissolution or biodegradation media and wherein the catheter shaft isconfigured to be withdrawn through the patient's vessel when thescaffold is in its expanded configuration.
 10. The system of claim 9,wherein the stent is self-expanding.
 11. The system of claim 9, furthercomprising a slidable tubular sheath surrounding the stent in thecollapsed configuration on the catheter shaft, said tubular sheathprotecting the coating or a shell from exposure to the dissolution orbiodegradation media.
 12. The system of claim 9, further comprising aninflatable balloon disposed between the stent and the catheter shaft,said balloon fracturing the coating or shell upon inflation.
 13. Thesystem of claim 12, wherein the balloon is sealingly attached to both aproximal end and a distal end of the catheter shaft.
 14. The system ofclaim 12, further comprising a slidable tubular sheath surrounding thestent in the collapsed configuration on the catheter shaft, wherein theballoon is constructed such that a force of friction of the balloon incontact with the stent is greater than a force of friction of the sheathin contact with the stent.
 15. A method for delivering a stent to atreatment site, comprising the steps of: providing an implant deliverysystem having a stent mounted on a catheter shaft, said stent having ascaffold with a coating or a shell surrounding the scaffold andretaining the scaffold in its collapsed configuration, and a tubularsheath surrounding the stent in the collapsed configuration on thecatheter shaft; advancing the implant delivery system to the treatmentsite; withdrawing the tubular sheath to expose the coating or shell to adissolution or biodegradation media; and withdrawing the catheter shaftfrom the treatment site.
 16. The method of claim 15, wherein the stentis self-expanding.
 17. The method of claim 15, wherein the deliverysystem further comprises a balloon interposed between the stent and thecatheter shaft, the method further comprising the step of inflating theballoon to cause expansion of the stent before withdrawing the cathetershaft.
 18. The method of claim 17, wherein inflating the ballooncomprises pressurizing a balloon inflation lumen with fluid or gas untila force of sliding friction of the stent against the balloon exceeds aforce of sliding friction of the stent against the tubular sheath.
 19. Amethod for delivering a stent to a treatment site, comprising the stepsof: providing an implant delivery system having a stent mounted on acatheter shaft, a balloon interposed between the stent and the cathetershaft, and a tubular sheath surrounding the stent in the collapsedconfiguration on the catheter shaft; advancing the implant deliverysystem to the treatment site; inflating the balloon to cause expansionof the stent before withdrawing the tubular sheath; withdrawing thetubular sheath; and withdrawing the catheter shaft from the treatmentsite.
 20. The method of claim 19, wherein the stent is self-expanding.21. The method of claim 19, wherein inflating the balloon comprisespressurizing a balloon inflation lumen with fluid or gas until a forceof sliding friction of the stent against the balloon exceeds a force ofsliding friction of the stent against the tubular sheath.